function timestampToDatetime(value) {
    if (value === undefined || value === null || value === '') {
        return '-';
    } else {
        let date = new Date(value);
        let year = date.getFullYear();
        let month = date.getMonth() + 1;
        let day = date.getDate();
        let hour = date.getHours();
        let minute = date.getMinutes();
        let second = date.getSeconds();
        month = month < 10 ? '0' + month : month;
        day = day < 10 ? '0' + day : day;
        hour = hour < 10 ? '0' + hour : hour;
        minute = minute < 10 ? '0' + minute : minute;
        second = second < 10 ? '0' + second : second;
        return year + '-' + month + '-' + day + ' ' + hour + ':' + minute;
    }
}

function strToTimestamp(str) {
    str = str.replace(/-/g,'/');
    return new Date(str).getTime();
}